Reinforced grinding wheel



Jan. 6.,.1970 S', 5 msTLlER ET AL. 3,4'87g590 RELNFORGED GRINDING WHEEL Filed F'eb. 2, 1967 .5112255 25727 Jue 00 /000 j ,2220 4000 TM-4! Eil ff 5%- Pff je f f e' 4f" agg 7% @gi United States Patent O 3,487,590 REINFORCED GRINDING WHEEL Samuel S. Kistler, Salt Lake City, Utah, Charles V. Rue,

Tillin, Ohio, and Frederick Fyfe, Jackson, Mich., as-

signors to International Telephone and Telegraph Corporation, New York, N.Y.

Filed Feb. 2, 1967, Ser. No. 613,578 Int. Cl. B24d 5/02 U.S. Cl. 51-206 5 Claims ABSTRACT F THE DISCLOSURE A grinding wheel for operation at high speed containing a centrally located high strength arbor ring bonded to the abrasive structure of the grinding wheel by. an adhesive material having a minimum shear strength of at least 1000 p.s.i. at a temperature of about 200 F. and higher; and, the method of making the grinding wheel.

Background of the invention This invention relates to high speed grinding wheels and reinforcement to permit safe operation at speeds in excess of present commercial practice.

In the present grinding wheel art the rotational speed of the wheel is an important factor in its performance. In general an increase in speed is accompanied by an increase in the rate of metal removal and an increase in the ratio of metal removal to wheel wear. Other effects also may be observed such as an increase or decrease in vibration, an increase in the apparent hardness of the wheel, etc. There thus is frequently found an optimum speed, especially for precision grinding, which may vary from one make of grinding machine to another.

The present invention is concerned with wheels in the snagging category. These wheels universally show improved performance with increase in speed and no upper limit has yet been observed to this rule in tests that have been made at speeds in excess of 30,000 s.f.p.m. (surface feet per minute), more than 3 times the normal operating speed of 9-500 s.f.p.m. This speed has been dictated by safety considerations, and in general it is felt that to go to higher speeds the snagging wheels should have increased strength.

The operating speed of 9500 s.f.p.m. was established years ago when strengths were not as great as they are now, so that it is practical to increase operating speeds to perhaps 12,500 s.f.p.m.safely. However, by reinforcement of the wheels with braided fiberglass it is now safe to operate them up to 14,600 s.f.p.m. (see U.S. Patent No. 3,123,948).

To go to still higher speeds safely a diterent kind of reinforcement is advantageous. Inthis method a steel hub or ring is cemented into the hole of the wheel to provide tension on the hole. When the wheel is standing still there may be no tension but at high rotating speeds the wheel will strive to expand more than the hub both due to its low modulus of elasticity, roughly only about one twentieth of that of steel, and to the smaller mean radius of the steel hub. Thus a tension on the wheel will develop through the cement helping to resist rupture.

This phenomenon was extensively studied and described in detail by Otto Kienzle and Klaus Greiner in Festigkeitsuntersuchungen and Klebverbindungen Zwischen Schleifund Tragkorpern, Forschungsberichte des Landes Nordrhein-Westfalen No. 844, Westdeutscher Verlag, Koln und Opladen, 1960.

Summary of the invention Broadly stated the present invention comprises a grinding wheel for operation at high speeds of rotation com- 3,487,590 Patented Jan. 6, 1970 prising an outer abrasive member, a centrally located high strength support ring, and an adhesive material for bonding the ring to the member having a minimum shear strength of at least 1000 p.s.i. at a temperature of 200F. and higher; and, in another aspect the present invention comprises the method of making said grinding wheel.

Brief description of the drawings FIGURE 1 is a graph illustrating the reduction in tangential stress (St) in a 24 inch diameter grinding wheel when various support rings or hubs are bonded to the wheel to give a radial pull of 1000, 2000, and 3000 p.s.i.;

FIGURE 2 is a graph illustrating variation of the bursting speed versus radial thickness of the support ring or hub of the grinding wheel; and

FIGURE 3 shows a grinding wheel in accordance with the invention containing a support ring cemented into the hole of the wheel.

Detailed description FIGURE l illustrates the stresses at the abrasive hole for a steel mill snagging wheel, for example of 24 inches diameter, 3 inches width measured along the rotational axis, and with a central hole through the wheel of approximately l2 inches to hold the support ring bonded to the wheel. By varying the radial thickness of the steel ring in the hole, the tension on the hole can be varied, while holding the rotational speed of the wheel constant at 3800 r.p.rn., as shown in FIGURE l.

FIGURE 2, curve A, shows the calculated bursting speed for a 24 inch O.D., l2 inch I.D., 3 inch wide snagging 4wheel with a steel ring cemented into the hole, assuming that the strength of the cement is at least equal to the strength of the wheel structure. FIGURE 3, curve B, shows the same calculation in which the pull of the ring on the wheel hole is 1000 p.s.i.

FIGURE 3 shows a grinding wheel in accordance with the invention designated 10. The abrasive portion 16 of the wheel is adhered or cemented with bonding material 14 to the support 12 which may be termed a ring, hub, arbor, sleeve or the like. Support 12 has a radial thickness 18, and the inside radius of the abrasive portion or the outside radius of the supportis designed r1, whereas r2 indicates the outside radius of the grinding wheel 10. The width of the wheel, not shown, is measured along the rotational axis.

By varying the radial thickness of the steel ring in the hole the tension on the hole can be varied at a given speed, as shown in FIGURE 1.

In FIGURE 3, curve A shows the calculated bursting speed for a 24" x 3" X l2" snagging wheel with a steel ring cemented into the hole, assuming that the strength of the cement is at least equal to the strength of the wheel structure. Curve B shows the calculation in which the pull of the ring on the wheel hole is 1000 p.s.i.

There is no thickness of ring that will not provide some reinforcement, and no ring material that will not have some benecial effect. Preferably the material for the ring is selected from the group of steel, iron, and aluminum.

The eiectiveness of the ring material is greater the greater is its modulus of elasticity, and of course it can only provide reinforcement to the extent of its strength.

If the ring is cemented into the wheel while both are hot, as in a curing oven, a high coelicient of expansion of the ring is helpful since on cooling to room temperature the ring, shrinking more than the wheel, will generate a tension, thus providing prestressing. To illustrate, the coefficient of expansion of steel is close to that of a hard grade snagging wheel so that on cooling from a curing temperature there will be little stress developed. Having a high elastic modulus, the steel will resist stretching and provide a high radial stress at high speed.

On the other hand an aluminum ring, having a coefficient of expansion twice that of the wheel will on cooling provide a strong tensile stress. Its modulus of elasticity, on the other hand is only one third of that for steel so that at high speed the reinforcement due to rotation will be less than that expected from steel. Putting the two effects together, aluminum and steel rank close together.

In view of the work done by Kienzle and Greiner, and the above considerations, the discovery of the present invention involves the reinforcement of a grinding wheel by a strong ring or hub using a highly heat resistant cement; and this heat resistance has been found to be uniquely important, since in severe snagging operations the hole of the wheel becomes highly heated by the bearing friction. This is something that these authors failed to ind and t our knowledge has not `been studied by anyone else. Our invention, then, lies in the discovery of a combination grinding wheel structure utilizing a support ring bonded to the wheel such that a minimum tensile shear strength between ring andy wheel of 1000 p.s.i. is obtained at temperatures of about 200 F. and higher.

The bonding material, cement, or adhesive material used to join the support or ring to the grinding wheel, is very important to obtain successful practice of the invention. The bond must have high strength at elevated temperature. As mentioned, the material used should be one which provides a high strength bond which gives a tensile shear break not less than about 1000 p.s.i. at a temperature in the range of about 200 F. or higher. If such a material is used this will prevent failure of the grinding wheel in operation from the heat of grinding or from heat transmitted from the grinder bearings.

Where the central ring is metallic, it is important that proper surface treatment is provided to secure adequate bonding to the abrasive structure. Such surface treatments are well known in the art and may include cleaning, pickling, priming, sand-blastig and the like.

The high temperature shear strength of some bonding materials or adhesives tested for use in the invention and found suitable are tabulated below:

*R.T. equals room temperature.

The procedures used to bond, cement or adhere a support or ring to the grinding wheel are several in number and can satisfactorily be any of those described below:

(1) The grinding wheel should lbe fully cured, bored out to receive a central ring and cement is applied to the I.D. of the wheel and the O.D. of the hub ring; the hub is pushed into place and the entire assembly recured at 350 F. Although this method gives excellent bonding strength, it is not as economical as those next described hereinbelow. However, this procedure does give suitable results and may be used for both resinoid and vitried wheels.

(2) For resinoid wheels, one satisfactory technique is to press the wheel such that it has the correct hole size when initially preparing the wheel, then a cement such as the 3M Companys EC 2086 cement is placed on the interior surface of the hole of the wheel before the resinoid bonding material has been cured, but after the wheel has been pressed. A high strength ring is then placed in the hole of the wheel and the normal wheel curing temperature of about 350 F. acts at one and the same time to cement the arbor ring to the abrasive structure of the wheel and also to cure the resinoid material forming the abrasive fbond.

(3) Another alternative for the preparation of resinoid bonded grinding wheels in accordance with the invention, and what is considered the most economical and foolproof method of preparing the wheel is to coat the O D. of the high strength ring with a high temperature cement such as 3M Company cement EC 2086. The cement coated ring is then placed in a pressing mold in which the wheel is to be pressed to shape and the abrasive mixture is then pressed or formed around the hub ring. The hub and wheel are stripped from the mold as a unit and cured as a unit. The curing process again functions to cure the fwhcel and the cement at the same time using a temperature of approximately 350 F.

(4) Another alternative method involves the application of this invention to the method of making resinoid bonded grinding wheels described in U.S. Patent No. 2,860,961, issued to Gregor et al. In this method, the central ring is treated with a cement in accordance with the invention, such as for example 3M Companys cement EC 2086, to provide proper adhesion to the thermosetting yresin bond of the grinding wheel which is formed around the ring said ring then becoming an integral part of the grinding wheel.

Tests were conducted with three sets of wheels to determine the effect of cementing in a steel arbor ring with heat resistant cement. Test Series Nos. 1 and 2 represent characteristic heavy duty steel mill snagging wheels, both of standard type and the steel arbor ring type in accordance with the invention; and Test Series Nos. 2 and 3 represent the type of resin bonded wheels known in the art which are used in foundries on iioor stand grinders and which are much lsofter and weaker than steel mill snagging wheels.

TEST SERIES NO. 1

Wheel size-24 x 3" x 12": Specification 7A123 Z1 BV3 (Grinding Wheel Institute designation, standard method of marking grinding wheels).

(a) Standard wheel breaking speed: 3800 r.p.m. or 23,800 s.f.p.m.

(b) Identical wheel but hole bored to 12.940 inches and steel sleeve 12.920 inches x 3 inches x 12.01 inches cemented into the hole of the wheel with 3M adhesive EC 2086 and cured at 350 F. Result: the breaking speed was above 4600 r.p.m. or 28,900 s.f.p.m.

TEST SERIES NO. 2

Wheel size-24" x 3" x 12": Specification 7A121 Zl BVS.

(a) Standard wheel breaking speed 23,800 s.f.p.m.

(b) Same specification except for steel arbor ring 12.920 inches x 3 inches x 12.01 inches bonded in place by method (4) (see U.S. Patent No. 2,860,961) gave breaking speeds of 28,890; 27,960; and 29,450 s.f.p.m. for three separate wheels.

A third series of 24 x 3" x l2" foundry wheels were prepared in which a range of relatively weak specifications were employed. The results for standard and steel arbor ringed wheels are given in Table No. 2. The results show a highly marked improvement for the steel arbor ring wheels of the invention.

7 VA143 O5 BL2-R-.- Standar 18, 200 8. VA143 O5 BL2-R Steel arbor ring 27, 500

*Grinding Wheel Institute designation.

There has been described herein the advantages of a new and unique article or grinding wheel and a method of reinforcing and preparing the wheel such that it is suitable for high speed rotational applications. The preparation includes the use of a high strength support or ring for the abrasive article which support is adhered, cemented or bonded into the hole of the article with a bonding material to provide a high strength bond giving a tensile break which is not less than about 1000 p.s.i. at 200 F. Also included is a method of prestressing grinding wheels which comprises heating the support or ring to an elevated temperature prior to its being bonded in place within the central part of the grinding wheels.

The disclosure of this invention is not to be limited to the exact and specific details as presented here but is to include such variations as do not depart from the spirit of the invention. For example, the support or central hub or ring need not be a single cylinder but may be made of square or rectangular cross section rings stacked to give the same effect as a single steel hub or ring. Even round cross section rings may be stacked and used as a supporting central hub with acceptable results when the proper adhesive bond is used. Also, the hub described herein may be located at any point between the arbor hole and the portion of the abrasive article which can be used in grinding. Although many different uses will be envisioned by those skilled in the art for the improved article described herein other than for snagging wheels and the like as described above, it should be understood that no limitation of the utility of the article should be placed on this invention, and for example, other abrasive articles can be equally satisfactorily reinforced as taught herein, and these would include vitrited bonded, rubber bonded, shellac bonded, silicate bonded, magnesite bonded and all types of articial resin bonded Wheels.

By the term ring as used herein it is mean the central hub, ring, or like structure as described above, and which is generally used in supporting the abrasive wheel of this invention such that it can be mounted for rotation.

Hence, while it will be apparent that the preferred embodiments of the invention disclosed are well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modication, variation, and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. A grinding wheel for operation at high speeds of rotation comprising an outer generally cylindrical and solid abrasive member, a centrally located high strength support ring means for supporting said member, and an adhesive material for bonding the ring means to the member having a minimum shear strength of at least about 1000 p.s.i. at a temperature of about 200 F. and higher.

2. The grinding wheel of claim 1 wherein said ring means has dimensions to support a radial stress of at least about 1000 p.s.i. on its periphery.

3. The grinding wheel of claim 2 wherein said ring means is made of a material selected from the group consisting of iron, steel, aluminum and aluminum alloys.

4. The grinding wheel of claim 1 wherein said abrasive member is a mixture of abrasive particles and a resinoid bonding material.

5. The grinding wheel of claim 4 wherein said ring means is made of a material selected from the group consisting of iron, steel, aluminum and aluminum alloys.

References Cited UNITED STATES PATENTS 642,828 2/ 1900 Spohn 51-206- 2,072,051 2/1937 Van der Pyl 51--206 2,121,656 6/1938 Fischer 51-206 2,446,817 8/ 1948 Feiler 51-206 3,206,894 9/ 1965 Schaffner 51-236 3,241,267 3/1966 Block 51--336 ROBERT C. RIORDON, Primary Examiner D. G. KELLY, Assistant Examiner 

